This application claims the priority of German patent document 102 05 415.0, filed Feb. 9, 2002, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device and method for use in the relative adjustment of the angle of rotation of a camshaft of an internal combustion engine with respect to a drive wheel. Preferred embodiments of the invention relate to the use of hydraulically actuated actuating elements for adjusting the relative rotational angle of the camshaft and drive wheel.
Various devices used in camshaft adjustment are known in the art (see e.g., the textbook “Fachkunde Kraftfahrzeugtechnik” [Handbook of Motor Vehicle Technology], 26th Edition, 1999, pages 272, 273). Two different designs of a camshaft adjustment device are described in the cited literature. In a first design, the exhaust camshaft drives the intake camshaft via a chain drive. Via the hydraulic adjustment of a chain tensioner arranged between the chain drive, the turning position of the intake camshaft can be shifted relative to the exhaust camshaft, allowing the valve timing to be adjusted as desired. In a second design of a camshaft adjustment device, it is provided, for example, that the intake camshaft is twisted relative to the camshaft drive wheel. In this example, a hydraulic piston that can be shifted to the left or the right is provided, whose axial movement in a mechanical adjustment unit with a helical gear effects an adjustment of the camshaft in the “advanced” or “delayed” direction. In addition to the above-described designs, so-called vane-cell camshaft adjusters are known (see e.g., EP 1 008 729 A2 corresponding to U.S. Pat. No. 6,302,072) in which the camshaft can again be adjusted relative to the camshaft drive wheel. The common factor in all of the above-named designs of a camshaft adjustment device is that the adjustment is accomplished hydraulically, wherein hydraulic lines that lead to two different pressure spaces or pressure chambers are provided, via which the actual actuating element of the camshaft adjuster can be shifted as desired to the left or to the right with the help of a control valve.
As is commonly known, with camshaft adjustment on the intake side, for example, the cylinder charge can be substantially improved over a broad speed range. In order to accomplish this, however, it is necessary for a hydraulic adjustment system of this type to operate with short delay times, or to guarantee a high adjustment speed. The adjustment speed of the camshaft adjuster is limited, however, because the oil that is required for loading pressure into the hydraulic chambers must first be drawn from an oil tank, e.g., the oil pan of the internal combustion engine. The problem with this is that at high oil temperatures, a smaller quantity of oil is available due to increased leakage in the oil lead; this reduces the speed of adjustment of the camshaft adjuster.
It is thus an object of the invention to improve the feed of hydraulic oil to a camshaft adjuster, in order to enable more rapid response or reaction times to camshaft adjustment.
This object is attained according to the invention by providing a controlled bypass arranged between the pressure chamber of the camshaft adjuster.
According to certain preferred embodiments of the invention, because a bypass line that can be controlled via a valve element is provided between the two control lines that lead to the pressure chambers of the camshaft adjuster, under certain operating conditions of the internal combustion engine, the oil that flows out of the depressurized hydraulic chamber can be fed directly to the pressurized control line or pressure chamber, avoiding the oil tank. In this manner, despite higher oil temperatures, the speed of adjustment of the camshaft adjuster can be improved relative to the known systems.
In certain preferred embodiments of the invention, the activation of the connection that exists between the two pressure chambers takes place in particular when the oil pressure in the non-activated pressure chamber of the adjustment unit is greater than the oil pressure in the activated pressure chamber that is being supplied with oil via a hydraulic line for adjustment of the camshaft. These pressure conditions can be present when an additional amount of torque is acting upon the camshaft in the direction of adjustment; a moment of rotation of this nature can be generated, for example, by closing the valves in the transfer to cam and camshaft, and thus to the adjustment unit.
Further advantages and advantageous improvements on the invention are disclosed in the claims and in the description.
In certain preferred embodiments of the invention, in a first advantageous design, the bypass that connects the two pressure chambers is integrated directly into the camshaft adjustment unit. This involves a so-called vane-cell camshaft adjuster, in which an inner component (rotor) is connected to the camshaft so that it cannot rotate, which rotor has vanes that extend from it at least nearly radially and are encompassed by a drive wheel, and has several cells that are distributed around its periphery and are separated by fixed members, so that, in each case, two pressure chambers are formed between the vanes of the inner component and the fixed members of the drive wheel. With this design, which is integrated into the camshaft adjuster, the hydraulic fluid can be conveyed via the shortest pathway from one pressure chamber to another. This allows extremely short adjustment times to be realized.
In certain preferred embodiments of the invention, a particularly compact construction that has low losses from leakage is achieved when the valve pin that is necessary for the shifting of the bypass system that is integrated into the camshaft adjuster is positioned in the inner component (rotor) of the adjustment unit.
In certain preferred embodiments of the invention, in one vane of the inner component, four bores are provided that serve to hold the valve pins. With the interaction of the four valve pins, on one hand, the oil supply from the oil tank to the two pressure chambers, and on the other hand, the bypass between the two pressure chambers, are controlled.
In certain preferred embodiments of the invention, in an advantageous manner, one valve pin is also designed as a locking element that acts between the inner component and the drive wheel.
In certain preferred embodiments of the invention, in a second advantageous design, the valve-controlled bypass is integrated between the two pressure chambers in the control valve.
In certain preferred embodiments of the invention, a simple and reliable shifting of the bypass that is integrated into the solenoid-control valve is characterized in that two valve actuators are arranged on a valve pin so that they can shift, and in that the valve actuators are provided with ring collars that control openings that lead to the control lines.
In certain preferred embodiments of the invention, in a third advantageous design, a reversing valve is provided in an oil tank line that leads to the control valve, which reversing valve is connected via a controllable line connection to a second oil tank line. In this manner, a controllable bypass between the two control lines that lead to the two pressure chambers is produced.
Three exemplary designs of the invention are described in greater detail in the following description and drawings.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.